1. Field of the Invention
This invention relates to alkylation catalysts. It is particularly concerned with a novel type of zeolite catalysts which exhibit a high degree of para selectivity in alkylation and transalkylation reactions.
2. Description of the Prior Art
Zeolite catalysts which have been modified by deposition thereon of a small amount of magnesium and phosphorus are known to promote the alkylation of aromatic compounds with a high degree of selectivity to the para isomer of the dialkylated benzene. See, for example, U.S. Pat. Nos. 4,011,276 and 4,098,837 to C. Chu and U.S. Pat. No. 4,128,592 to W. W. Kaeding.
Unfortunately, it has been found that the desirable para selectivity of these very unusual and useful catalysts can be adversely affected (i.e. the catalyst is "deselectivated") during normal use and storage. While the overall alkylation and disproportionation activity of the catalyst is generally unaffected, the selectivity to the desired para isomer in the product is reduced dramatically. Attempts to regain the para selectivity by conventional methods, such as drying and calcining to remove adsorbed water from the deselectivated catalyst, have been unsuccessful.